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How to match light bulb wattage to light fixtures

Updated: May 20, 2021

When you change a light bulb, do you check the ratings on the light fixture first to make sure the wattage is correct? In all likelihood, you are like most people and simply grab whatever spare light bulb you might have on hand. Or if the light fixture doesn't seem bright enough, you might replace a 60-watt bulb with a 100-watt bulb. This could be a serious safety hazard, though.

An often-overlooked but critical electrical safety issue is making sure the wattage ratings on your light bulbs do not exceed the ratings of the light fixtures.

The Danger

Light fixture sockets all have maximum wattage ratings, and if you exceed the recommended ratings by installing bulbs that have higher wattage ratings, there is a definite chance that excess heat generated by the bulbs might scorch insulation. It could melt the insulating jackets on wires or cable sheathing—or even overheat wooden framing, in the case of canister recessed light fixtures.

Light Fixture Ratings

Generally speaking, the maximum wattage ratings are printed on the light-bulb sockets themselves. You will see language that reads something like: "Caution: Use only Type A lamp, Maximum 60 watts." In some cases where a fixture has two or more light bulbs, there may be a total wattage rating for the entire fixture. In this case, you'll need to make sure that the total wattage of all the light bulbs added together does not exceed the maximum rating of the light fixture. The goal here is to make sure that the combined heat of all light bulbs is not enough to damage the light fixture or penetrate through the insulation.

Symptoms to Watch For

Anytime you detect a burning odour or see scorch marks on a light fixture; it's a sign you may be exceeding the wattage rating of the light fixture. Shut off the light and have an up-close look at the fixture.  If it feels very warm to the touch, that's a danger sign. At this point it's not enough just to replace the bulb with one of lower wattage—you also need to check to make sure there's been no permanent damage.

Remove the mounting screws, pull the light fixture away from the electrical box, and inspect the wires inside. If you see melted or scorched wire nuts or insulation on the wires or cable sheathing, there's been some serious damage, and you should have an electrician inspect things and reconnect the wiring. He or she will probably cut away damaged wires and reconnect them properly.

A table or floor lamp is also susceptible to damage from light bulbs that are larger than they should be. If the shade on a lamp is hot to the touch or has become damaged by heat, inspect the light bulb wattages and make sure they match the socket ratings. If the sockets themselves are scorched, they will need to be replaced. And while you're at it, make sure the lamp wire itself has not been damaged; rewire the lamp if necessary.

What About CF or LED Light Bulbs?

The compact fluorescent (CF) and light-emitting diode (LED) light bulbs that have begun to replace incandescent bulbs are usually labelled in a manner that tells you how they compare to standard light bulbs. The packaging usually says something like "75 watts (uses only 11 watts)."

For purposes of matching light-bulb wattage to socket ratings, it is the smaller, actual wattage ratings of CF and LED bulbs you need to be concerned with. In other words, if you have a lamp with maximum socket ratings of 60 watts but find that you don't have enough light in the room, replacing the incandescent light bulbs with "75 watts" LED bulbs that use only 11 watts is a perfectly safe practice.

Do not think, however, that CF or LED light bulbs do not emit any heat at all. While the glass bulb itself is considerably cooler to the touch than standard incandescent bulbs, the metal base on these bulbs does get quite warm. Generally speaking, though, CF or LED bulbs with standard screw-in ends can safely be used with standard light fixture sockets (known as Edison sockets).

Timothy Thiele | 7 November 2018

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